1. Field of the Invention
The invention relates to production of colour image screens and somewhat more particularly to a method of producing a patterned opaque layer on screen substrates.
2. Prior Art
A method of producing black edging about phosphor dots on a screen substrate so as to form a light-absorbing matrix surrounding the color phosphors is known, for example as described in German Offenlegungsschrift 25 26 882. In accordance with this disclosure, a filter layer is formed from dimethyl-dicarbocyanine-paratoluene sulfonate in a carrier of nitrocellulose and solvent of acetone, and is applied, together with phosphor materials and a photoresist material to a screen surface, photographically exposed by forward and backward exposure and then developed.
Other methods of producing black or opaque edging are also known, for example as disclosed by I Oshishi et al, IEEE Transactions On Electron Devices, Vol. ED-22, No. 9, September 1975, pages 650-653. Generally, the there-disclosed method comprises applying a black-colored insulating layer on a screen surface and photo-etching sites or windows therein for the color phosphors. Prior to applying such layers, which, for example, are composed of lamp black (soot) or carbon black (graphite), the substrate surface must first be sub-layered with a photosensitive layer over its total area. Further processing then proceeds so that layer segments from the substrate remain on the sites pre-selected for later application of the phosphor pigments and, after the black edging is applied, such layer segments are underetched with H.sub.2 O.sub.2 and rinsed away with water so that windows for the color phosphors are formed.
Black or opaque edging must exhibit the following characteristics:
1. It must be highly light absorptive; PA0 2. It must have good adhesion to screen substrates; PA0 3. It must have good mechanical loadability; PA0 4. It must have a long operating life; and PA0 5. It must be sufficiently conductive to maintain a screen potential during excitation of such screen by a cathode ray.
The prior art methods of producing black or opaque edging about phosphor dots on image screens are relatively complicated and are uneconomical. Further, such prior art methods only partially provide the above-referenced characteristics, especially in regard to adhesive strength and mechanical loadability.